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Abstract

We previously reported a Doppler optical coherence tomography (DOCT) system design [1] for high-speed imaging with wide velocity dynamic range (up to 28.5 dB when acquiring 8 frames per second), operating at 1.3 µm with a coherence length of 13.5 µm. Using a developmental biology model (Xenopus laevis), here we test the DOCT system’s ability to image cardiac dynamics in an embryo in vivo, with a simple hand-held scanner at 4 ~ 16 frames per second. In particular, we show that high fidelity DOCT movies can be obtained by increasing the reference arm scanning rate (~8 kHz). Utilizing a combination of four display modes (B-mode, color-Doppler, velocity variance, and Doppler spectrum), we show that DOCT can detect changes in velocity distribution during heart cycles, measure the velocity gradient in the embryo, and distinguish blood flow Doppler signal from heart wall motions.

Figures (7)

(a) Schematics of the hand-held probe, incorporating a fiber probe at the end of a SMA-28 fiber, and a rotor disk connected to a galvanometer scanner. (b) Details of the fiber probe. An angle-polished GRIN lens with ~ 1 mm working distance is bonded to the polished fiber end using optical cement. The entire assemble is housed in a steel sheath of 1.1 mm outer diameter.

DOCT video [480 kB with audio] of a stage 47 Xenopus tadpole, imaging the left and right aortic branches (L and R), acquired at 8 fps. (a) Structural (B-mode) video of the aortic branches cross-section. Notice a smaller vessel (V) in the video. Bar = 500 µm. (b) 2× zoom of the yellow rectangular region in (a), showing the micro-structure of L. The break in the yellow line indicates the location from which Doppler spectrum information is collected and encoded into audio format (see Fig. 4), demonstrating the velocity distribution within L. Bar = 250 µm. (c) Color-Doppler video, showing the corresponding velocity map in the cross-section. Notice the low noise background, and the pulsatile blood flow in L and R. The Doppler angle (α) is estimated to be ~ 63° for R. The small blood vessel (V) is much better visualized in the color-Doppler mode, allowing estimation of its diameter to be less than 70 µm. Systole occurs during the 4th and 5th frames, where the velocity gradients in R are visible, and the peak Doppler shift is ~ 9 kHz considering aliasing effects. (d) Velocity variance video, showing the increased variance of the blood flow within L and R. Each individual image was recorded at 450×508 pixels, and re-sampled into 256×160 pixels for video compression. The faint horizontal line in (a), (c), and (d) was an artefact probably due to multiple-reflection.

Doppler spectral display of the DOCT system. The full Doppler spectrum represents the velocity distribution of the blood flowing within the analysis window, which is the gap in the yellow line shown in Fig. 3(b). Notice the rapid onset of systole and the aliasing caused by the peak velocity (arrows), as well as the relatively longer time for diastole (heart relaxation).

(a) Real-time (32 fps) B-mode OCT video [914 kB] of the Xenopus heart, showing the ventricle (V), atria (A), and the truncus arteriosis (TA). (b) Same video played back at 10 fps [246 kB], allowing better visualization of the motion dynamics, as well as the spiral valve (SV) in TA and the trabeculae carneae (T) network in the ventricle. Static frames in (c)–(e) illustrate different phases of the heart cycle, showing the sequence of atria filling in (c), atria contraction (AC) and ventricle filling in (d), and ventricle contraction (VC) which pumps blood through the truncus arteriosis in (e). Acquired at 225×508 pixels before re-sampling for video compression. Scale bar = 500 µm.

DOCT video of the stage 46 Xenopus tadpole heart, acquired at 8 fps [305 kB]. (a) Structural video showing the ventricle (V) and truncus arteriosis (TA). The atria are also visible in the video (not shown in this static frame). Scale bar = 500 µm. (b) Color-Doppler video showing the blood flow (B) within the ventricle and the truncus arteriosis. Notice the homogeneous distribution of Doppler shift in the ventricle wall (VW) and the truncus arteriosis wall (TAW). The partial division at the center of truncus arteriosis is probably the spiral valve (SA), also showing homogeneous Doppler shift distribution, distinct from the blood flow. A small blood vessel can also be seen in the video (not shown in this static frame). (c) Velocity variance video showing the blood flow (B). The blood flow, spiral valve, and the truncus arteriosis wall are better visualized in the 2 × zoom videos, shown in structural mode (d), and velocity variance mode (e). Acquired at 450×508 pixels per frame before re-sampling for video compression.